In the manufacture of semiconductor devices, ion implantation is used to dope wafers and/or workpieces with impurities or dopants. Ion beam implanters are used to treat silicon workpieces with an ion beam, in order to produce n or p type extrinsic material or to form passivation layers during fabrication of an integrated circuit. When used for doping semiconductors, the ion beam implanter injects selected extrinsic ion specie to produce the desired semiconducting material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in “n type” extrinsic material workpieces, whereas if “p type” extrinsic material workpieces are desired, ions generated from source materials such as boron, aluminum or gallium typically are implanted.
Ion implanters are also used in non-doping applications which may use ion beams of elements such as hydrogen or helium. An example of a non-doping application is wafer splitting which is enabled by creating a buried hydrogen layer in the silicon and then removing the top silicon layer in subsequent thermal processing steps. Typical hydrogen production ion implantation systems have unique parameters that separate them from the majority of implants performed in a standard high current implanter. One such parameter is the implant energy. As compared to typical high current implanters the energies are higher in order to produce a sufficiently deep implanted layer. Secondly, the dose requirements are higher than with typical implants in the range of 1×1016 ions/cm2 to 1×1017 ions/cm2. To support sufficiently high production output, the high doses require the implantation system to operate with 30 ma-60 ma of beam current, for example.
Traditional ion implantation equipment for semiconductor processing requires elemental mass selectivity in order to implant the desired specie into the workpiece and reduce the level of contamination resulting from other elements. The mass selectivity is accomplished with the use of electromagnets to bend the charged ion beam and then pass the beam through a mass selection resolving aperture. Together with the beam envelope and the electromagnets, the resolving aperture size and shape also determines the elemental resolving capability of the ion implanter. The size and shape of the aperture affects the selected mass resolution and cross-sectional envelope of the ion beam.
Typical high current implanters with horizontal dispersive planes are designed with rectangular resolving apertures which unevenly clip the ion beam. In conjunction with the mass analysis electromagnet, the width of the aperture typically defines the mass resolution of the system while the height of the aperture simply defines the maximum height of the beam at the workpiece target. Systems may be designed with additional beam forming and shaping apertures upstream or downstream of the resolving aperture which further define the final size of the ion beam at the workpiece. These apertures typically cause some uneven beam intercept as the beam passes through the openings.
Thus, there remains a need for improved systems and methods for reducing particles and contamination by matching beam defining aperture shapes to the ion beam shapes in the ion implantation systems.